The invention concerns a method of making a lever-type cam follower out of thin-walled light-weight sheet metal for loading at least one gas exchange valve of an internal combustion engine, said cam follower comprising two side walls which, together with a crossbeam that connects these side walls to each other, form a U-shaped cross-sectional profile pointing away from the gas exchange valve, the cam follower further comprising two finger-like tabs for receiving a stem end of the gas exchange valve, which tabs are configured on one end of the cam follower as extensions of the side walls and are bent through 180xc2x0 onto an undersurface of the crossbeam.
The invention further concerns a flat sheet metal blank for forming a lever-type cam follower for loading at least one gas exchange valve of an internal combustion engine, said blank, as seen in a top view, having a substantially rectangular geometry, and two-finger-like tabs extending from one end of the blank being configured as mirror images of each other in respect of a central longitudinal axis of the blank.
A cam follower of the pre-cited type disclosed in DE-OS 198 11 658 comprises two finger-like tabs on one end. The tabs are configured as extensions of the side walls of the cam follower and are bent onto its undersurface. A gas exchange valve can be received between the tabs. Punching-out of the blank for making the cam follower results in the production of an unnecessarily large amount of chippings. This is due to the relatively large length of the tabs. In the prior art, a blank of this type is punched out of a sheet metal strip, with the tabs having a straight and parallel configuration (see, for example, DE-OS 198 10 462, FIG. 4). This unnecessarily increases the length of the blank. As a result, only a disproportionately small number of blanks can be cut from a given length of strip. The aforesaid chippings unnecessarily increase the material costs.
It is a first object of the invention to provide a method of making a lever-type cam follower out of thin-walled light-weight sheet metal which avoids the initially described drawbacks with simple measures.
It is a second object of the invention to provide a sheet metal blank which avoids the initially described drawbacks with simple measures.
These and other objects and advantages of the invention will become obvious from the following detailed description.
The invention achieves its first object by the fact that the method comprises the following steps, which may be supplemented with further intermediate steps:
a) punching out a blank out of sheet metal with the tabs being bulged outward in arc-shaped curves that are configured as mirror images of each other in respect of a central longitudinal axis of the cam follower,
b) bending or deep drawing the side walls so that the side walls extend at right angles to the crossbeam, and
c) bending the tabs onto the undersurface of the crossbeam.
The invention achieves its second object by the fact that the tabs are bulged outward in arc-shaped curves that are configured as mirror images of each other.
Due to the arc shape of the tabs the length of the blank is markedly shorter than that known from the prior art. This results in a significant reduction of punching waste. This is particularly remarkable if the blank is cut out of a sheet metal strip. It must further be noted that due to the bending radius already included in the tabs, the final bending of the tabs onto the undersurface is not only simpler but also gentler to the material.
Ends of the tabs comprise extensions that serve as welding studs for connection to the undersurface of the crossbeam following the bending-over of the tabs onto this undersurface. This is a simple manner of achieving an excellent positional fixing of the tabs on the cam follower in the crosswise direction of the cam follower.
Due to the fact that the vertices of the tabs that point with their ends preferably towards a central longitudinal axis of the blank are situated within a cutting width of the blank, it is possible to use a relatively narrow sheet metal strip. The width of the entire work-piece holding device is thus likewise advantageously minimized.
The proposed U-shape of the cam follower endows this with an excellent rigidity. The invention is primarily directed to a cam follower configured as a finger lever or a rocker arm but can equally well be implemented on an oscillating arm.
Although the invention proposes an outwards bulging arc-shape of the tabs, it is also conceivable to make the tabs with an inward bulge so that their vertices are situated in directly opposing relationship to each other.
The ends of the tabs of the flat blank are spaced from each other to a certain extent. This spacing is to be seen as a compulsory width required for the punching tool. Further, it is also possible to make the outer sides of the tabs not directly as extensions of the long sides of the blank, as claimed, but to arrange them slightly offset inwards relative to the end of the blank.
Conceivable and within the scope of the invention are also a variety of cross-sectional profiles of the cam follower including completely or nearly flat profiles.
For a better understanding, the invention is described below with reference to the appended drawings.